Two strains of Dunaliella, a unicellular, biflagellate, wall-less green alga, are capable of producing very large amounts of β-carotene, Dunaliella salina Teod. and Dunaliella bardawil(1). D. bardawil is a halotolerant alga whose β-carotene content comprises about 50% all-trans-β-carotene with the remainder composed mostly of 9-cis β-carotene and a few other β-carotene isomers(2). A process has been described for cultivating D. bardawil so as to obtain algae containing up to about 5% by weight of β-carotene(3). Later developments of the process increased the percentage to more than 8%. It has been shown that the natural isomer mixture of β-carotene which is accumulated in the alga Dunaliella bardawil is accumulated in fatty tissues of rats and chicks to an extent which is about 10 fold higher than that observed by feeding the synthetic all-trans β-carotene(4).
Various carotenoid-enriched Dunaliella commercial products are available such as Betatene™ (produced by the Henkel Corp., Germany) and Nutrilite™ (Amway, Inc., U.S.A.). These products are oil extracts of carotenoids from Dunaliella. 
Retinoids are essential for a living organism for vision, cellular growth, differentiation, and to maintain the general health of the organism. 9-cis-retinoic-acid and all-trans-retinoic-acid are produced in the body by the cleavage of β-carotene (BC). The retinoid nuclear receptors, also known as orphan receptors RAR and RXR, have distinct physiologic properties by activating transcriptional factors. All-trans retinoic-acid binds to RAR but not to RXR, while 9-cis retinoic-acid binds to RXR, which plays a key role in important biological processes.
The activation of nuclear receptors is essential to cell metabolism, especially with respect to lipids and glucose. Several nuclear receptors have been implicated in cholesterol homeostasis. These receptors include: the liver X receptors (LXRa/NR1H3 and LXRb/NR1H2) and farnesoid X receptor (FXR/NR1H4) that are bound and activated by oxysterols and bile acids, respectively. LXR and FXR form obligate heterodimers with RXR that is activated by 9-cis retinoic acid and synthetic agonists (termed rexinoids). It was recently found that the activation of RXR by its ligands can affect two central processes of cholesterol metabolism: I. Cholesterol absorption in the intestine (activation of RXR/FXR heterodimer repressed cholesterol 7α-hydroxylase (CYP7A1) expression, resulting in decreased bile acid synthesis and cholesterol absorption). II. Reverse cholesterol transport from peripheral tissues (activation of RXR/LXR heterodimer inhibited cholesterol absorption and induced reverse cholesterol transport in peripheral tissues).
The following nuclear receptors are known to form heterodimers with RXR and hence, can be potentially activated by 9-cis retinoic acid administration: thyroid hormone (TRa/b); vitamin D (VDR); fatty acid/eicosanoids (PPARα/βγ); oxysterols (LXRa/b); bile acids (FXR); pregnanes/bile acids/xenobiotics (PXR); androstanes/xenobiotics (CAR).
Fibrates (clofibrate, fenofibrate, bezafibrate, ciprofibrate, beclofibrate and gemfibrozil) are currently recommended for the treatment of patients with hypertriglyceridemia (high plasma TG). The treatment of hypertriglycerdemia results in decreased plasma levels of triglyceride-rich lipoproteins. HDL cholesterol levels are usually increased when the baseline levels are low. The increase in HDL cholesterol is usually concomitant with increased levels of the HDL apolipoprotein A-I and A-II. In addition, fibrates reduce the atherogenic apoC-III-containing particles, effect post-prandial lipemia and some fibrate lower plasma fibrinogen and CRP levels.
As a consequence of their effect on lipid metabolism, fibrates have been shown to affect specific lipoprotein disorders such as in combined hyperlipidemia, primary hypertriglyceredemia, type III dysbetalipoprotenemia, and non-insulin dependent diabetes mellitus (NIDDM).
Fibrates are considered to be well tolerated, with an excellent safety profile. A low toxicity has been reported in almost every organ system. Fenofibrate treatment revealed low frequency of side effects. Long-term administration revealed no effect on peroxisome proliferation in human liver and no evidence for carcinogenesis. Clinically relevant interaction of fibrates with other anti-hyperlipedemic drugs include rhabdomyolysis and decreased bioavailibility when combined with some bile acid sequestrants. Potentiation of the anticoagulant effect of coumarin may cause bleeding.
Fibrates mediate at least part of their effects by peroxisome proliferator-activated receptor α (PPAR-α). Upon activation with fibrates, PPARs heterodimerize with another nuclear receptor, the 9-cis retinoic acid receptor (RXR). The dimer binds to specific response elements, termed peroxisome proliferator response elements (PPREs) and regulates gene expression.
Low plasma levels of high-density lipoprotein (HDL) and high triglyceride (TG) plasma levels are risk factors for atherosclerosis. Low levels of plasma HDL cholesterol, apolipoprotein AI (apoA-I) and high levels of triglycerides (TG) are associated with increased risk for atherosclerosis, the major cause of morbidity and mortality in Western societies. A recent study showed that the rate of coronary events is reduced by 22 percent by raising HDL cholesterol levels and lowering the plasma TG levels in patients treated with the fibrate gemfibrozil.
Several modes of action were proposed for the fibrate beneficial effects on atherosclerosis: Induction of lipoprotein lipolysis by reducing apoC-III levels and/or by increasing lipoprotein lipase activity. Induction of hepatic fatty acid (FA) uptake by the induction of FA-transporter protein and acyl-CoA synthetase. Decrease apoB and VLDL production. Reduction of hepatic TG production by induction of peroxisome (in rodents only) or mitochondrial β-oxidation pathway and inhibition of FA synthesis. Most important, fibrates increase the production of apoA-I and apoA-II in the liver, which probably contribute to the process of reverse cholesterol transport.
Type 2 diabetes mellitus is a serious health problem. It arises when resistance to the glucose lowering effects of insulin combines with impaired insulin secretion to raise the levels of glucose in the blood beyond the normal range. Thiazolidinediones are a new class of antidiabetic agents that improve insulin sensitivity and reduce plasma glucose and blood pressure in subjects with type 2 diabetes(5). The drugs bind and activate PPARγ that binds to DNA as heterodimers with a common partner, retinoid X receptor (RXR) to regulate transcription. RXR agonists have been shown to function as insulin sensitizers, markedly decreasing serum glucose, triglycerides and insulin in obese mice(6).
WO 93/24454 describes a carotenoid composition derived from Dunaliella algae in which the β-carotene content is predominantly 9-cis β-carotene. There is no mention of any medical applications.
U.S. Pat. No. 5,219,888 (Katocs) discloses a method to increase plasma HDL levels for the treatment and prevention of coronary artery disease by administrating a therapeutic amount of the retinoids all trans-retinoic acid and 9-cis-retinoic acid.
U.S. Pat. No. 5,948,823 discloses use of a substantially crude Dunaliella algae preparation in protecting mammals against the detrimental effects of medical and nuclear irradiation.
WO 97/10819 teaches a new treatment for non-insulin dependent diabetes mellitus by administration of RXR agonists and optionally, peroxisome proliferation activated receptor gamma agonists.
WO 99/50658 identifies compounds which modulate nuclear receptor activity, used for treating e.g. cancer, cardiovascular disease, osteoporosis, diabetes, postmenopausal disorders and inflammatory conditions.
WO 2001119770 reveals new retinoid X analogs, useful as retinoid X receptor modulators for lowering blood glucose levels, for modulating lipid metabolism and in treatment of e.g. diabetes, obesity, cardiovascular diseases and breast cancer.
U.S. Pat. Nos. 5,972,881 and 6,028,052 (Heyman) disclose methods and compositions for the treatment of non-insulin dependent diabetes using an RXR agonist together with a PPARγ agonist.
WO 03/027090 provides novel retinoid compounds that have selectivity as RXR agonists, and are effective in reducing blood glucose and maintaining body weight, thus being useful for the treatment of diabetes (NIDDIM) and obesity.
Colagiuri S. and Best, J. Lipid-lowering therapy in people with type 2 diabetes. Current Opinion in Lipidology (2002) 13:617-623, teaches that lipid powering with statins and fibrates is effective in improving cardiovascular disease outcome in diabetes.
Levy, Y. et al. Dietary supplementation of a natural isomer mixture of Beta-carotene inhibits oxidation of LDL derived from patients with diabetes mellitus. Nutrition & Metabolism (2000) 44:54-60, describes experiments in which Dunaliella bardawil-derived β-carotene was supplemented to the diet of diabetic patients. The dietary supplementation normalized the enhanced LDL susceptibility to oxidation in these patients.